This invention relates to an ion exchange operation wherein increased flow rates can be employed.
In many ion exchange systems, a moving stream containing exchangeable ions is flowed through an ion exchange resin bed. Generally, the rate of flow of such liquid through the resin bed is as high as possible in order to obtain the greatest use of the ion exchange bed per unit of time. However, in downflow-type systems, this rate of flow is often limited by the rate at which the ion exchange resin can exchange ions (i.e., the kinetics of the resin). When the flow rate is too high, some or all of the ions desirably removed from the liquid flow past the ion exchange bed before the resin can remove them. Thus, "leakage" of the ions is seen. This leakage is generally highly undesirable. In conventional ion exchange systems, this leakage is cured by reducing the flow rates of the liquid through the column, by increasing the length of the column, or by adding additional column(s) to the system.
In upflow-type systems, a major limitation of this system has been the low density of conventional ion exchange resins. Because of this low density, the resin bed would be swept upward by the rising liquid and out of the column. Recently, higher density ion exchange resins have been developed which have highly crosslinked or brominated copolymer matrices in order to reduce this loss of resin in upflow-type systems. Unfortunately, however, it has been found that in many applications the expected increase in the operating flow rates when such high density resins are employed cannot be achieved without substantial leakage of the ions by the column. Such leakage is due to the slow kinetics of these higher density resins.
Accordingly, an ion exchange system which can be operated at high flow rates without substantial leakage or loss of resin, would be highly desirable.